1. Field of the Invention
The present invention relates to image pickup apparatuses having pixels including photoelectric conversion units and analog-digital converting units.
2. Description of the Related Art
From the past, an image pickup apparatus has been known which includes a pixel part having pixels in a matrix form which perform photoelectric conversion and output a signal based on incident light and a column array analog-digital converting part having analog-digital converting units corresponding to columns of pixels (hereinafter, an analog-digital converting unit will be called an ADC (Analog Digital Converter) and a column array ADC will be called a column ADC. In the column ADC, an ADC of each column performs analog-digital conversion (hereinafter will be called AD conversion) which converts an analog signal output from a pixel (hereinafter called a pixel signal) to a digital signal.
An example of the column ADC which has been known has a plurality of comparators which compare a ramp signal and a pixel signal and a counter which counts clock pulse signals. Japanese Patent Laid-Open No. 2011-217206 discloses an image pickup apparatus having a column ADC which compares signals output by a plurality of comparators.
Japanese Patent Laid-Open No. 2011-217206 discloses an image pickup apparatus including a first pixel, a second pixel, a first comparator provided for the first pixel and a second comparator provided for the second pixel, and a difference circuit connected to the first comparator and the second comparator, and a counter. The counter counts clock pulse signals on the basis of a difference signal output from the difference circuit and thus generations a count signal. A comparison result signal output by the first comparator is a signal indicative of a result of a comparison between a signal output from the first pixel and a ramp signal that is a signal having a potential that changes depending on a time. In the same manner, a comparison result signal output from the second comparator is a signal indicative of a result of a comparison between a signal output from the second pixel and a ramp signal. The difference circuit outputs to a counter a difference signal that is a signal which operates the counter during a period from a change of a signal value of a comparison result signal that is a signal indicative of a one comparison result by the first or second comparator to an inversion of the other comparison result signal. The counter counts clock pulse signals during a period while a difference signal is being output from the difference circuit.